1. Field of the Invention
The present invention relates to an exposure control method and apparatus for use with video cameras, and more particularly to an exposure control method and apparatus wherein photometry is carried out by using a video signal outputted from an image area sensor which picks up scene images.
2. Description of the Background Art
As an exposure control method for a camera, there is known a method as disclosed in Japanese Patent Laid-open Publication No. 62-203141. According to this method, an image frame is divided into a central area and a plurality of concentric peripheral areas surrounding the central area, and the size of a main object in the image frame is estimated on the basis of the distance to the main object, such as a person, and the focal length of the taking lens. If the main object has a size substantially equal to the central area, an exposure correction amount is obtained using the outputs from the central area and peripheral areas. The exposure correction amount, added to a value center-weighted averaged over all light readings obtained through weighted addition of photometric values at respective areas, is used as an exposure value according to which the exposure control is carried out. This exposure control method obtains the exposure correction amount in accordance with the relationship between a main object and the luminance of the background thereof. It is therefore possible to obtain a proper exposure even for a rear light scene or the like.
The above conventional exposure control method, however, is associated with a problem that if a main object is located displaced from the center of the image frame, the influence of background luminance becomes significant so that a proper exposure control cannot be attained precisely. Further, with this exposure control method, a proper exposure cannot be obtained of the face of a person wearing clothes such as white or black, of which the reflective index is largely different from that of the face. Still further, in the case of a rear light scene and in the case of a spot light scene with a main object spot-lighted, it is difficult to obtain a proper exposure control of a face of person. Furthermore, if the size of a main object changes frequently in respective scenes due to motion of the main object, the exposure correction amount changes at corresponding frequency, resulting in an unnatural exposure control.